Optical devices such as optical waveguides and switches are used in communications and data transfer equipment to transfer information from one location to another and to switch the information to a desired output. The information is in the form of a continuous or a pulsing optical signal.
These optical devices contain a core or cores made of a material that transmits light of the desired wavelength and cladding that abuts at least one side of a core. Optical waveguides are used to carry optical signals from one location to another. Multiple cores are used to form e.g. switches to switch an optical signal to a desired output core, filters to filter one or more optical signals of a particular wavelength, or multiplexers to combine or separate optical signals of different wavelengths. Optical cores can be linear, but often optical cores must curve in order to direct a signal from one location to another within the confines of a small space.
One major objective of electro-optic device research is to reduce the size of components. There are two benefits from reducing the size of components: (1) devices such as waveguides and electro-optic switches are shorter and/or smaller, allowing more components to be placed within an integrated device; and (2) signals are transmitted between components more quickly, which increases the speed at which data is transferred.
Currently, if the direction of an optical signal is to be changed 90.degree., the core must be fabricated to have a radius of approximately 10 mm to avoid losing much of the optical signal to the cladding in the curved section. Consequently, every 90.degree. turn that is incorporated along the length of a device adds at least 10 mm to the length or width of the device.
Another objective of electro-optic device research is to provide components that can be manufactured such that their switching characteristics are more consistent, so that a switch fabricated today performs essentially the same as a switch fabricated a month or year from today. Many switches have switching characteristics that are extremely sensitive to the voltage of the signal used to switch the optical signal from one output core to another or to distribute the optical signal among multiple cores. These switches are quite sensitive to manufacturing variances, and significant variations occur from one batch to the next of these switches or even within a batch of these switches.
An interferometric modulator as illustrated in FIG. 1 is a modulator whose performance is extremely sensitive to the voltage used to modulate the optical signal. This type of switch can be fabricated by diffusing a metal such as titanium into an electro-optic crystal such as LiNbO.sub.3 to form the cores. The titanium-diffused portion of the crystal (which is also electro-optic) has a higher refractive index than the virgin portion of the crystal, and consequently, the titanium-diffused portion acts as cores which carry an optical signal.
The interferometric modulator 100 as illustrated in FIG. 1 uses multiple cores to modify an input optical signal. The input optical signal is split between two input cores 110 and 120, and the two input cores separate from one another a sufficient distance that the cores do not evanescently couple. The optical signal in core 110 travels through that core unmodified. The second core 120 has a set of electrodes 130 fabricated above it, so that an electric field can be applied to the electro-optic material in that core. The optical signal in the second core can be unmodified as it travels through the core, or the optical signal can have its phase shifted in response to the electric field created by electrodes above and on either side of the core. The two cores subsequently recombine to form one core, where the optical signals add to one another. If the optical signals from each core are in phase in the section where the cores recombine to form one core, the signals add to form an optical signal having the same wavelength and phase. If the optical signals are out of phase, the optical signal that is output depends on how much the phase of the signal was shifted as it traveled through core 120.
The interferometric modulator of FIG. 1 can be very difficult to fabricate consistently. The amount of titanium diffused into the crystal is highly dependent on processing conditions, and the minor variations in processing conditions that occur during normal manufacturing processes cause an interferometric modulator produced in one batch to function very differently from an interferometric modulator made in another batch of switches when an identical electric field is applied to both switches.
It is an object of this invention to provide hybrid waveguide structures such as optical waveguides that have improved properties such as greater isolation, tight turning radii, or different propagation characteristics. It is another object of this invention to provide hybrid waveguide structures such as electro-optic switches that have less variance in their intended use because of the switch design and/or because of the process by which the switches are manufactured.